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Title: Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries

Abstract

In this paper, we report on the synthesis of poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), via cationic ring-opening polymerization of the cyclic ether monomer, 1,3,6-trioxocane. We use a combined experimental and computational approach to study ion transport in electrolytes comprising mixtures of P(2EO-MO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Mixtures of poly(ethylene oxide) (PEO) and LiTFSI are used as a baseline. The maximum ionic conductivities, σ, of P(2EO-MO) and PEO electrolytes at 90 °C are 1.1 × 10 –3 and 1.5 × 10 –3 S/cm, respectively. This difference is attributed to the T g of P(2EO-MO)/LiTFSI (-12 °C), which is significantly higher than that of PEO/LiTFSI (-44 °C) at the same salt concentration. Self-diffusion coefficients measured using pulsed-field gradient NMR (PFG-NMR) show that both Li + and TFSI ions diffuse more rapidly in PEO than in P(2EO-MO). However, the NMR-based cation transference number in P(2EO-MO) (0.36) is approximately twice that in PEO (0.19). The transference number measured by the steady-state current technique, t +,ss, in P(2EO-MO) (0.20) is higher than in PEO (0.08) by a similar factor. We find that the product σt +,ss is greater in P(2-EO-MO) electrolytes; thus, P(2EO-MO) is expected to sustain higher steady-state currents under dc polarization, makingmore » it a more efficacious electrolyte for battery applications. Molecular-level insight into the factors that govern ion transport in our electrolytes was obtained using MD simulations. These simulations show that the solvation structures around Li + are similar in both polymers. The same is true for TFSI . However, the density of Li + solvation sites in P(2EO-MO) is double that in PEO. Finally, we posit that this is responsible for the observed differences in the experimentally determined transport properties of P(2EO-MO) and PEO electrolytes.« less

Authors:
 [1]; ORCiD logo [2];  [3]; ORCiD logo [2];  [4];  [2]; ORCiD logo [5]; ORCiD logo [1]; ORCiD logo [6]
  1. Cornell Univ., Ithaca, NY (United States). Dept. of Chemistry and Chemical Biology. Baker Lab.
  2. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Science Division
  3. Purdue Univ., West Lafayette, IN (United States). Charles D. Davidson School of Chemical Engineering
  4. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering
  5. California Inst. of Technology (CalTech), Pasadena, CA (United States). Division of Chemistry and Chemical Engineering
  6. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Science Division. Energy Storage and Distributed Resources Division
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1461983
Grant/Contract Number:  
AC02-05CH11231; CHE-1335486
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 51; Journal Issue: 8; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE

Citation Formats

Zheng, Qi, Pesko, Danielle M., Savoie, Brett M., Timachova, Ksenia, Hasan, Alexandra L., Smith, Mackensie C., Miller, Thomas F., Coates, Geoffrey W., and Balsara, Nitash P. Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries. United States: N. p., 2018. Web. doi:10.1021/acs.macromol.7b02706.
Zheng, Qi, Pesko, Danielle M., Savoie, Brett M., Timachova, Ksenia, Hasan, Alexandra L., Smith, Mackensie C., Miller, Thomas F., Coates, Geoffrey W., & Balsara, Nitash P. Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries. United States. doi:10.1021/acs.macromol.7b02706.
Zheng, Qi, Pesko, Danielle M., Savoie, Brett M., Timachova, Ksenia, Hasan, Alexandra L., Smith, Mackensie C., Miller, Thomas F., Coates, Geoffrey W., and Balsara, Nitash P. Tue . "Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries". United States. doi:10.1021/acs.macromol.7b02706. https://www.osti.gov/servlets/purl/1461983.
@article{osti_1461983,
title = {Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries},
author = {Zheng, Qi and Pesko, Danielle M. and Savoie, Brett M. and Timachova, Ksenia and Hasan, Alexandra L. and Smith, Mackensie C. and Miller, Thomas F. and Coates, Geoffrey W. and Balsara, Nitash P.},
abstractNote = {In this paper, we report on the synthesis of poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), via cationic ring-opening polymerization of the cyclic ether monomer, 1,3,6-trioxocane. We use a combined experimental and computational approach to study ion transport in electrolytes comprising mixtures of P(2EO-MO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Mixtures of poly(ethylene oxide) (PEO) and LiTFSI are used as a baseline. The maximum ionic conductivities, σ, of P(2EO-MO) and PEO electrolytes at 90 °C are 1.1 × 10–3 and 1.5 × 10–3 S/cm, respectively. This difference is attributed to the Tg of P(2EO-MO)/LiTFSI (-12 °C), which is significantly higher than that of PEO/LiTFSI (-44 °C) at the same salt concentration. Self-diffusion coefficients measured using pulsed-field gradient NMR (PFG-NMR) show that both Li+ and TFSI– ions diffuse more rapidly in PEO than in P(2EO-MO). However, the NMR-based cation transference number in P(2EO-MO) (0.36) is approximately twice that in PEO (0.19). The transference number measured by the steady-state current technique, t+,ss, in P(2EO-MO) (0.20) is higher than in PEO (0.08) by a similar factor. We find that the product σt+,ss is greater in P(2-EO-MO) electrolytes; thus, P(2EO-MO) is expected to sustain higher steady-state currents under dc polarization, making it a more efficacious electrolyte for battery applications. Molecular-level insight into the factors that govern ion transport in our electrolytes was obtained using MD simulations. These simulations show that the solvation structures around Li+ are similar in both polymers. The same is true for TFSI–. However, the density of Li+ solvation sites in P(2EO-MO) is double that in PEO. Finally, we posit that this is responsible for the observed differences in the experimentally determined transport properties of P(2EO-MO) and PEO electrolytes.},
doi = {10.1021/acs.macromol.7b02706},
journal = {Macromolecules},
issn = {0024-9297},
number = 8,
volume = 51,
place = {United States},
year = {2018},
month = {4}
}

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